Provided is a method of planarizing a semiconductor device. The method includes providing a substrate. The method includes forming a first material layer on the substrate. The method includes forming a second material layer over the first material layer. The second material layer is softer than the first material layer and has an exposed surface that is not in contact with the first material layer. The method includes flattening the second material layer without removing a portion of the second material layer. The flattening is carried out in a manner such that the exposed surface is substantially flat after the flattening. The method includes performing an etch back process to remove the second material layer and a portion of the first material layer. Wherein an etching selectivity of the etch back process with respect to the first and second material layers is approximately 1:1.